In use, an ink ribbon of an ink ribbon cassette is subjected to sequential interrupted movement during the starting of the letter or symbol carrying part of the machine as well as by the ribbon drive assembly. To ensure that the ink ribbon is guided at a uniform height portion in front of the letter or symbol carrying part, attention has been directed to the rotation of the ribbon feed shaft.
In U.S. Pat. No. 4,034,935, there is disclosed the use of a layer or strip of foam material disposed proximate the ribbon feed coil or support plate therefor in a manner to engage the ribbon feed coil or support plate of the assembled ink ribbon cassette to thereby retard the rotational movement of the ribbon feed coil during use. While the use of foam material is effective in retarding rotational movement, the placement and/or thickness of the foam material results in uneven forces. Aging of the foam material may also effect uniform operation.
In German application DE-GM No. 80 02 752, there is disclosed the use of a rubber band guided around an extension or shoulder on the shaft of the feed ribbon coil and a cooperating stationary pin or projection. Another solution is the use of a metallic V-shaped coil spring including an upright pin portion positioned on the shaft of the feed ribbon coil wherein the ribbon is coursed about the upright pin of the metallic coil. The metallic material forming the coil spring is subject to many variable factors during manufacturing thereby resulting in uneven force during use.
In the aforementioned copending application, there is disclosed a braking device for a ribbon supply spool and formed of a planar V-shaped plastic device disposed on a shaft of the ribbon supply spool and comprised of a ring-shaped portion from which extend leg portions wherein one leg portion is formed with an upright pin and wherein a portion of the ring-shaped portion opposite the leg portions is formed of reduced cross-sectional area, preferably in a line bisecting an angle formed by the leg portions.